This invention relates to fuel impervious coated articles and more particularly, to epoxy-based fuel resistant coatings on polyethylene substrates.
It is known to manufacture a wide variety of articles such as fuel tanks especially canisters or automobile fuel tanks, from suitable polymeric materials, such as polyethylene. Recently, this technology has assumed increased importance because of its suitability for maximizing space utilization, such as the inaccessible dead spaces present in automobile bodies. This is so since in order to maximize space usage the tanks must be designed with complicated configurations, consequently, tank manufacture from sheet metal is either expensive or impossible. However, such articles are easily produced utilizing, for example, extrusion blow molding methods. Additionally, the low weight of the polymeric fuel tank is particularly advantageous, particularly regarding fuel economy. However, a disadvantage of these articles is that the synthetic resins suitable for utilization as fuel tanks, such as polyethylene, exhibit an undesirable permeability to the hazardous fuels.
It has been suggested to reduce this permeability through the fluorination or irradiation of the polymeric article. Sulfonation has also been disclosed (DAS No. 1,953,371), but this process is burdened by expensive process steps on account of the necessity to drive off the excess sulfur trioxide present, and the subsequent neutralization. Consequently, the problem of reducing the permeability of polymer fabricated fuel tanks still remains a troublesome one for the art.
Although the concept of improving the tanks by a simple varnishing is a known solution, it has been found that a variety of varnish systems including those based on polyvinylidene fluoride, polyvinyl alcohol, and polyamide 6 in conjunction with a variety of primers all exhibit either inadequate fluid barrier properties or unsatisfactory substrate adhesion after being exposed to the presence of the fuel for extended time periods.
Consequently, it is quite surprising to discover that this problem can be solved through the usage of a three-component varnish coat, without the presence of a suitable primer or adhesion promoter, in the manner as set forth herein.